That there would a sabotaging of or attack on the GPS satellites rather than atomic EMF event.

If there was a major EMF event (either from a major cosmic or nuclear "exchange"), then our receivers and a lot of electrical gear would be compromised. I guess if your Loran was off and hiden away, then maybe...

But the least of our problems would be our chart plotters. ;^)))

https://www.youtube.com/watch?v=vuP6KbIsNK4